Sweetening of petroleum distillates



Patented July 31, 1951 SWEETENING F PETROLEUM DISTILLATES John G.Browder, Houston, and Alvin R. Smith,

Baytown, Tex., assignors, by mcsne assignments, to Standard OilDevelopment Company, Elizabeth, N. J a corporation of Delaware NoDrawing. Application March 23, 1950,

. Serial No. 151,516

' 11 Claims.

The present invention involves contacting a sour petroleum distillatehaving a boiling range of about 200 to 750 F. to which has :been added asmall amount of methyl alcohol and betanaphthol in catalytic quantitywith a solution of an alkali metal hydroxide to form a mixture thereofand maintaining the mixture undergoing contacting in the presence of amild oxidizing agent in an amount sufiicient to sweeten the distillate,following which the alkali metal hydroxide is separated from thecontacted distillate.

The invention is particularly adapted-to dis tillates boiling in therange from about 200 to 750 F. and has a special application tosweetening of kerosenes and the so-called solvent naphthas, the latterboiling in the range of 200 to 450 F.

The methyl alcohol may be employed in an amount in the range from about0.1 to about 2.5% by ,volume (based on the sour distillate) with apreferred amount in the range from about 0.5 to about 1% by volume. Thebeta-naphthol may be employed in amounts based on the sour.

distillate varying from about 0.05 to about 1.0 gram per liter, the sumtotal of the methyl alcohol and beta-naphthol not being in excess ofabout 3.0% by volume of the sour distillate to be sweetened. Thebeta-naphthol and methyl alcohol are preferably added to the petroleumdistillate, but may be added to the mixture of the alkali metalhydroxide and sour petroleum distillate undergoing a sweeteningreaction.

The alkali metal hydroxide employed in the present invention preferablyshould be a solution of an alkali metal hydroxide. Preferably thesolution should be an aqueous solution having a Baum gravity in therange of from about 30 "to about 50 Baum, but solutions of lowerstrength may be used under some conditions. An aqueous solution ofsodium hydroxide of 40 Baum has been found to give satisfactory resultsin the practice of the present invention. Other alkali metal hydroxidesbesides sodium hydroxide may be used. For example, lithium and potassiumhydroxidev may be used in lieu of sodium hydroxide, but the latter is tobe preferred.

The temperature at which the treating operation is conducted willusually be atmospheric and may range from about 60 F. up to 200 F. andsometimes higher temperatures may be employed depending on the boilingrange and the type of feed stock being treated. Apreferred temperaturerange may be from about to about atmospheric temperatures encountered inthe Texas Gulf Coast area. 7

The process of ouriinvention may be carried out in suitable equipmentwhich will allowv con-L tact of the sour distillateto. which methylalcohol and beta-naphthol have been added with the alkali metalhydroxide and the mild oxidizing agent. For example, pumps, jet mixers,incorpo rators and contacting towers'may' be used. Such towers may beequipped with packing, bell cap; trays and other similar well knownexpedients for insuring contact between liquids and between liquids andgaseous materiaL' The present invention' will be illustrated, fur: therby the following example:

EXAMPLE I A solvent naphtha having a copper number of less than 1 andhaving a boiling point in the range between 290 and 410 F. wasdividedinto 1 required to sweeten the naphtha. After water washing itwas also submitted to the above mentained tests. The third portion hadadded to it] 0.5% by volume based on the solvent naphtha of methylalcohol andthen contacted with sodium hydroxide solutionas mentionedbefore, in the presence of 300% by volume of the theo-,. retical amountof oxygenrequired to sweeten. The fourth portion had added to it 0.05%by volumeof methyl alcohol and was subjected to contact with sodiumhydroxide in the presence of 300% by volume of the theoretical oxygenrequired to sweeten same. The fifth portion had added to it 0.5 gram perliter of beta-naphthol and was then subjected: to contact withportions.- of the same sodium hydroxide solution inthe presence ofoxygen in the. excess amounts -in-., dicated before. The sixth portionhad added to it 0.1 gram of beta-naphthol per liter and was subjected tocontact with the same (sodium hydroxide) caustic solution in thepresence of 300% by volume of the theoretical amount of oxygen requiredto sweeten. The seventh and last por-- tion had added to it'0.05% byvolume of methylalcohol and 0.1 gram of beta-naphthol per liter;

and was subjected to contact with the same caustic solution in thepresence of 300% by volume of the theoretical amount of oxygen requiredto sweet-en. The results of these tests are It will be seen fromthefor'egoing results that the only treatment which caused the solventnaphtha to pass the doctor test was the one where both methyl alcoholand beta-naphthol were present. All of the other treatments reflectedthat the naphtha was =not sweetened by virtue of the fact that it didnot pass (DNP) the doctor test. It is of interest to note that thetreatments did not affect the color of the solvent naphtha whichremained at 30, the original color of the solvent naphtha being 30.Since the alcohol may have a detrimental effect on the flash point ofsolvent naphthas to which it and betanaphthol are added prior to contactwith caustic solution and oxygen, it may be desirable in the practice ofthe present invention to remove the alcohol. This may be effectivelydone by washing the sweetened product with water or by heating thesweetened product to remove methyl alcohol therefrom by simpledistillation. Neither one of the treating operations has any effect onthe color. A sample of the solvent naphtha treated in accordance withthe present invention as shown in column 7 of Table I was divided intothree portions. Each of these portions contained a small quantity ofalcohol by virtue of the alcohol having been added thereto inadmixturewith beta-naphthol. One portion was heated to 150 F., the second portionto 200 F. and the third portion to 250 F. The flash points and Sayboltcolors of the heated sweetened product were then determined and areshown in Table II:

1 About 80 F.

' It will be noted that heating the solvent naphtha to 150 F.effectively removed the alcohol, was indicated by the specificationflash point, and heating the solvent naphtha to as high as 250 F. didnot affect the color.

EXAIVIPLE II In order to illustrate further the synergistic effect ofmethyl alcohol and beta-naphthol in the practice of the presentinvention, a high sulphur refined oil raifinate, from solvent extractionof a hydrocarbon fraction in the kerosene boiling range, having a coppernumber of 40 was divided into eight portions. One portion was contactedwith 50 Baum sodium hydroxide solution as is in the presence of 300% byvolume of the theoretical amount of oxygen required to sweeten and thecopper number determines immediately after the treat and after 1, 3, 5and 24 hours settling. Three of the remaining seven portions had methylalcohol added to them in varying percentages and were also subjected totreatment with the sodium hydroxide solution in the presence of theaforesaid amount of oxygen. A fifth portion had beta-naphthol added toit and was also subjected to treatment in the presence of 300% by volumeof the theoretical amount of oxygen required to sweeten, while theremaining three portions had both methyl alcohol and beta-naphthol addedto them and were subjected to contact with the sodium hydroxide solutionin the presence of 300% by volume of the theoretical amount of oxygenrequired to sweeten. The results of these tests showing the coppernumber immediately after and after 1, 3, 5 and 24 hours of settling andthe percentage of reduction in copper numher after 24 hours arepresented in Table III:

Table III High Sulfur Refined Oil Raflinate of 40 Copper N umber 50 BaumCaustic, Per Cent. 1.0 1.0 1.0 1.0 1.0 1.0 1.0 MethylAlcohol,Vol. PerCent 0.05 0.1 0.2 0.05 0.1 0.2 B-NaphthoLgms/l 9.1 0.1 0.1 0.1 Oxygen,Per Cent of Theor.. 300 300 300 300 300 300 300 300 Copper No. AfterTreat:

- Immediately after 26 34 32 32 36 29 26 lhourafter 20 24 24 10 9 l03hoursalter 20 19 21 20 35 9 8 8 5hours after 21 16 8 5 7 24l1ours after22 10 10 6 15 2-3 2 2-3 Per Cent Reduction in Copper NumberAfter24Hours- 75 75 85 60 500.2'905002 It will be apparent from the datain Table In that treatment with sodium hydroxide solution in thepresence of oxygen results in only 45% reduction in copper number,whereas treatment with varying amounts of alcohol showed reductionsbetween 75 and 85% in the copper number. Treatment of the distillate towhich beta-naphthol had been added showed a reduction of about 60% ofthe copper number, while in the practice of the present invention asillustrated in columns 6 to 8 of Table III, reductions of about 90% wereeffected. It will be seen that the reduction of the copper number in thepractice of the present invention is greater than the average of thateffected by the methyl alcohol and the betanaphthol alone. Thus, itappears that the methyl alcohol and beta-naphthol when used together andadded to the sour raflinate has a synergistic effect thereon incatalyzing the sweetening operation.

The Saybolt colors shown in Example I were determined in accordance withthe ASTM Test method D156-38 while the flash point was determined inaccordance with the AS'I'M Test method D56-36.

In the foregoing examples, the improvement obtained by the practice ofthe present invention has been illustrated by the copper number test.This is a well known analytical procedure in the petroleum industry. Adescription of the method of test may be found in U. 0. P. LaboratoryTest Methods for Petroleum and Its Products, Third Edition, page I-I-6l,Universal Oil Products Co., Chicago, 1947. This test is a measure of thev mercaptan sulfur content of the oil being tested Although notillustrated by the several examples, one or the particular advantages ofthe of the alkali metal hydroxide solution. The

alkalimetal hydroxide appears to function as a true catalyst since thesmall amount used may be recycled to treat large quantities of the sourpetroleum distillate. A small amount of the alkali metal hydroxidesolution may be entrained in the treated naphtha, and, therefore, it maybe necessary to replace the entrained amount with fresh solution. Inshort, it is contemplated in the practice of the present invention thatthe alkali metal hydroxide solution will be reused over and over againsince it isnotnecessary to regenerate the alkali metalh'ydroxidesolution.

Hie invention has been described and illustrated by employment of a mildoxidizing agent such as oxygen. It is contemplated that mixtures ofoxygen with other gases, such as air may be employed. It is alsocontemplated that other mild oxidizing agents such as peroxides,permanganates, and the like may be used." For example, a hydrogenperoxide solution may be employed as the mild oxidizing agent.

In practicing the present invention, it is to be understood that thepetroleum distillate may be subjected to a preliminary treatment forremoval of hydrogen sulfide if the distillate contains hydrogen sulfide.Such preliminary treatment may include washing with a dilute alkalimetal hydroxide solution or blowing with a free oxygen-containing gas,such as air. If hydrogen sulfide or other acidic compounds are presentand not removed, the alkali metal hydroxide solution employed as thecatalyst may very quickly become seriously depleted in activity.

In the practice of the invention, it will be desirable to use an amountof oxygen in excess of the theoretical amount required to sweeten thesour petroleum distillate. Ordinarily, an amount of about 300% of thetheoretical amount to sweeten may be employed. However, sweetening inaccordance with the present invention may be obtained with considerablylesser quantities of oxygen. In other instances as much as 500% of thetheoretical amount required to sweeten may be employed. In fact,sweetening may be obtained in some cases by contact with the oxygenpresent in the treating vessel. It will be desirable to employ an amountof oxidizing agent at least equivalent to the theoretical amountrequired to sweeten.

I'he invention has been described and exemplified by employment of 0.5to 1% by volume of the catalytic alkali metal hydroxide solution. It iscontemplated that as little as 0.1 and as much as 5% by volume, or more,of the alkali metal hydroxide solution, based on the sour naphtha, maybe employed. Very good results. however. are obtained with 1% by volumeand this amount will be preferred.

It is to be understood that after separation of the alkali metalhydroxide solution the contacted naphtha may be washed with water, ifdesired. to remove any alkali metal hydroxide which may be entrainedtherein and to remove methyl alcohol when the fraction treated is asolvent naphtha or kerosene and where the presence of the alcohol mayhave a detrimental effect on the flash point thereof. In most instancesit will be unnecessary to treat the contacted naphtha with water orother aqueous solutions.

The nature and obiects of the present invention having been completelydescribed and illustrated, what we wish to claim as new and useful andsecure by Letters Patent is:

if'A' 'method for sweetening a sour petroleum distillate containingmercaptans boiling below 750 F. which comprises adding to saiddistillate an amount of beta-naphthol and methyl alcohol, said methylalcohol being employed in an distillate and then contacting saiddistillate containing methyl alcohol and beta-naphthol with a solutionof an alkali metal hydroxide while adding a sufiicient amount of a mildoxidizing agent to convert the mercaptans to disulfides and to obtain asweetened distillate.

2. A method for sweetening a sour petroleum distillate containingmercaptans boiling below 750 F. which comprises adding to saiddistillate an amount of beta-naphthol and methyl al-' cohol in therange, respectively, from 0.05 to 1 gram per liter of said'distillateand from 0.05% to 2.5% by volume based on said distillate, forming amixture of an aqueous solution of sodium hydroxide and said sourpetroleum distillate to which beta-naphthol and methyl alcohol have beenadded, and then agitating the mixture while adding a sufficient amountof a mild oxidizing agent to convert the mercaptans to disulfides and toobtain a sweetened distillate.

3. A method for sweetening a sour petroleum distillate containingmercaptans boiling below 750 F. which comprises adding to saiddistillate an amount of beta-naphthol and methyl a1- cohol in the range,respectively, from 0.05 to 1 gram per liter of said distillate and from0.05 to 2.5% by volume based on said distillate, forming a mixture of anaqueous solution of sodium hy droxide and said sour petroleum distillateto which beta-naphthol and methyl alcohol have been added, and thenagitating the mixture while adding a suificient amount of air to convertthe mercaptans to disulfides and to cause sweetening of said distillate,separating sodium hydroxide solution from said distillate and recoveringsaid distillate.

4. A method for sweetening a sour petroleum distillate containingmercaptans which comprises adding 0.2% by volume of methyl alcohol and0.1 gram per liter of beta-naphthol to said sour petroleum distillate,forming a mixture of said sour petroleum distillate to which methylalcohol and beta-naphthol have been added with an aqueous solution ofsodium hydroxide having a Baume gravity of 50, agitating the mixturewhile adding a sufficient amount of air to convert the mercaptans todisulfides and to cause sweetening of said distillate, separating saidsodium hydroxide solution from said agitated distillate, and recoveringsaid agitated distillate.

5. A method in accordance with claim 4 in which the amount of sodiumhydroxide solution is 1% by volume based on thesour distillate.

6. A method for sweetening a sour solvent naphtha containing mercaptanshaving a boiling point in the range between 200 and 450 F. whichcomprises adding to said solvent naphtha methyl alcohol in an amount inthe range between 0.1% and 2.5% by volume of said solvent naphtha andbeta-naphthol in an amount in the range between 0.05 and 1.0 gram perliter of said solvent naphtha, forming a mixture of an aqueous solutionof an alkali metal hydroxide and said solvent naphtha to which methylalcohol and beta-naphthol have been added and then agitating the mixturewhile adding a sufiicient amount ofia mild oxidizingvagentqtorconvertthe mercapta-nsto disu-Ifidesand to obtain. a sweetenededisti-11ate...

'7. A .method 'in, accordance. with claim 6 .inwhich the alkali metal:hydoxide is. sodium hydioxide.-

8. -A:method. .in accordance.yvith claim ..6 in. which the aqueousisolutionais.employedin an amount equivalent .to. approximately. 1 by.vol. ume .of .thersolvent naphtha.

9. .A .method. ..for.. sweetening .a sour solvent naphtha. containing,mercaptanshaving. a boilingopo int in the .range between 290? and 410 F.

while. maintaining the color of said. naphtha which comprises adding tosaid.s01vent naphtha 0.05% byvolume of methyl alcohol based on .the

s01vent.naphtha and. 0.1 'gr amof beta-naphthol...

per. liter of said naphtha forming amixture of an aqueous solution of.sodium hydroxide insaid.

solvent ..naphtha to. which methyl alcoholand air. -itot- :eonyertmercaptansi-toc disulfides. and-stow obtain a neweeteneddistillate,andyrremovingmethylalcohol from. said sweetened distillate-:1

10..A methoddnaccordance with -c1aim=.9 in 5 which themethy1=a1coho1-.isremoved by-;wash:

ing-the-sweetened naphtha with water.

1147A :method-in accordance with.c1aim- 9 Tin!"- which, themethyLalcohol is removed .by heating the sweetened naphtha-101atemperature. of. at-,

JOHN G. BROWDER ALVIN: R." SMITH.-

REFERENCES. CITED beta-naphthol have been added, then agitating U themixture while. adding a sufiicient amount of 2,494,687 I Bond., Jan.'17, 1950.,

1. A METHOD FOR SWEETENING A SOUR PETROLEUM DISTILLATE CONTAININGMERCAPTANS BOILING BELOW 750* F. WHICH COMPRISES ADDING TO SAIDDISTILLATE AN AMOUNT OF BETA-NAPHTHOL AND METHYL ALCOHOL, SAID METHYLALCOHOL BEING EMPLOYED IN AN AMOUNT IN THE RANGE BETWEEN 0.5% TO 2.5% BYVOLUME BASED ON SAID DISTILLATE, AND SAID BETANAPHTHOL BEING EMPLOYED INAN AMOUNT IN THE RANGE BETWEEN 0.05 AND 1 GRAM PER LITER OF SAIDDISTILLATE AND THEN CONTACTING SAID DISTILLATE CONTAINING METHYL ALCOHOLAND BETA-NAPHTHOL WITH A SOLUTION OF AN ALKALI METAL HYDROXIDE WHILEADDING A SUFFICIENT AMOUNT OF A MILD OXIDIZING AGENT TO CONVERT THEMERCAPTANS TO DISULFIDES AND TO OBTAIN A SWEETENED DISTILLATE.